1. Introduction
The abalone aquaculture industry along the eastern Pacific is located in areas that Ž
. support an abundance of wild kelp Macrocystis spp. or Nereocystis luetkeana . These
brown macroalgae are easily harvested feed for land-based and offshore abalone farms Ž
. Hahn, 1989; McBride, 1998 . Kelp supports relatively slow abalone growth rates,
Ž .
y1
Ž typically 30–60 mm shell length SL d
Ebert and Houk, 1984; Trevelyan et al., .
1998 , and limits the geographic expansion of the abalone industry to sites where kelp Ž
. can be harvested in large quantities Ebert, 1992 . Further, governmental regulation
Ž .
Ž Mercer et al., 1993; McBride, 1998 and natural events, such as El Nino Ebert, 1992;
˜
. McBride, 1998 , may reduce availability of harvested kelp.
As an alternative to the collection of wild algae, we investigated the potential of Ž
. cultivating the nutritious macroalgae dulse Palmaria mollis with the red abalone in a
land-based co-culture system. Dulse was determined to be an ideal candidate for land-based production due to ease of culture, rapid growth rate and capacity to absorb
Ž . Fig. 1. A Diagram of abalonerdulse co-culture system used for the 139-day growth trial. Water and algae
were tumbled via vigorous aeration from a perforated airline along the tank bottom. A circular abalone tank Ž
. was placed immediately above the airline. Tank sides were shaded so light ambient and supplemental entered
Ž
2
. Ž . the system only through the top surface area s 0.155 m . B Nitrogen and carbon cycle within the
abalonerdulse co-culture system.
Ž .
Ž .
dissolved nutrients Levin, 1991 . In addition, Buchal et al. 1998 found dulse to be highly nutritious, supporting abalone growth rates of up to 3.8 mm SL month
y1
. Ideally, in a self-sustaining co-culture system, abalone would consume dulse and
release both ammonia and carbon dioxide as waste. Dissolved abalone waste products would then be absorbed by the dulse, with inorganic carbon and nitrogen being
Ž .
assimilated into growing dulse tissue Fig. 1 . Traditional land-based abalone farms maintain water quality via rapid water exchange rates, which flush metabolic and other
waste products from the culture system. By contrast, dulse serves not only as a food source in co-culture, but also as an in situ biofilter. Therefore, dulse maintains water
Ž .
quality i.e., absorbs ammonia within the co-culture system, allowing water flushing rates to be minimized and operating costs reduced. Macroalgae have previously been
Ž reported to effectively reduce nutrients in aquaculture effluents e.g., Cohen and Neori,
. 1991; Shpigel et al., 1993; Krom et al., 1995; Neori et al., 1996 .
Maximum abalone stocking density within such a co-culture system could be limited Ž .
Ž . by 1 the amount of algae available for abalone to consume, and 2 the capacity of the
algae to absorb ammonia excreted by the abalone. Both limitations can be addressed by increased algal production rates which would supply more algae as fodder and increase
Ž dissolved nutrient uptake rates Neori et al., 1991; Magnusson et al., 1994; Braud and
. Amat, 1996 . Locations that lack year-round abundant natural sunlight, such as the
Pacific Northwest, may require supplemental artificial illumination to enhance algal production and therefore abalone yield.
This paper describes a series of experiments conducted at the Hatfield Marine Ž
. Science Center HMSC , Newport, Oregon, USA, which were designed to determine
limiting factors affecting the stocking density of red abalone in a co-culture system with Ž
. dulse. Experiments were carried out during Fall
August–October, 1996 , Winter Ž
. Ž
. Ž
November 1996–January 1997 , Spring March–April 1997 , and Summer May–July, .
1997 because season-dependent factors such as water temperature and solar radiation are major parameters affecting the co-culture system. Finally, the growth rates of
abalone within the co-culture system were measured.
2. Material and methods
Kategori